1. Field of the Invention
The present invention relates to an electronic fuel injection control in which the basic fuel injection quantity for each fuel injection valve of an internal combustion engine under a high load condition is controlled to control the air-fuel ratio (A/F).
2. Description of the Prior Art
In known electronically controlled fuel injection systems of the type which controls the opening time length of electromagnetic fuel injection valves for intermittently supplying fuel to an engine, for example, an electronically controlled fuel injection system of the mass flow type, the opening time length T of each electromagnetic fuel injection valve is computed from an equation T=t.sub.p .times.K.sub.1. Here, t.sub.p represents a basic fuel injection pulse width and it is determined by the division of an engine intake air quantity Q by an engine speed N. K.sub.1 represents a correction factor determined by outputs of various sensors, for example, a water temperature sensor, and t.sub.p is multiplied by K.sub.1 to provide a value of A/F which is purposely made to deviate from a value of A/F determined by a value of t.sub.p.
As regards the value of the basic fuel injection pulse width t.sub.p, it has been an usual practice to preset a fixed maximum value t.sub.pmax for the value of t.sub.p so as to prevent the misoperation of continuous fuel supply from occurring in the electromagnetic fuel injection valves for some reason or other.
A disadvantage of conventional electronically controlled fuel injection systems is that intake air pulsations occurring under a heavy engine load condition are transmitted directly to an air flow meter (an intake air quantity sensor), so that a measuring plate of the air flow meter is opened excessively due to its misoperation. As a result, a basic fuel injection pulse width t.sub.p, which exceeds a fuel supply quantity corresponding to an actual air flow quantity, is computed and an excessive quantity of fuel is supplied from the electromagnetic injection valve, thereby causing an over rich fuel mixture problem. Accordingly, it has been impossible to control the air-fuel ratio under heavy load conditions, thereby resulting in variations in the engine power output, etc. FIG. 6, which will be described later, shows an example of the relation between the over rich rate and the engine speed at the fully open throttle valve position in a conventional fuel injection system. It will be seen from the Figure that the conventional system has a disadvantage of increasing the over rich rate. This invention has been made with a view to overcoming the foregoing deficiencies of the prior art.